Battery construction having pressure release mechanism

ABSTRACT

An electrochemical cell constructed in accordance with the present invention includes a can for containing electrochemical materials including positive and negative electrodes and an electrolyte, the can having an open end and a closed end; a pressure relief mechanism formed in the closed end of the can for releasing internal pressure from within the can when the internal pressure becomes excessive; a first outer cover positioned on the closed end of the can to be in electrical contact therewith and to extend over the pressure relief mechanism; a second outer cover positioned across the open end of the can; and an insulator disposed between the can and the second outer cover for electrically insulating the can from the second outer cover. According to another embodiment, the second cover is dielectrically isolated from a current collector.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/102,951, filed Oct. 2, 1998, and U.S. Provisional Application No.60/097,445, filed Aug. 21, 1998.

BACKGROUND OF THE INVENTION

The present invention generally relates to an electrochemical cellconstruction. More particularly, the present invention relates to thecontainers and collector assemblies used for an electrochemical cell,such as an alkaline cell.

FIG. 1 shows the construction of a conventional C sized alkaline cell10. As shown, cell 10 includes a cylindrically-shaped can 12 having anopen end and a closed end. Can 12 is preferably formed of anelectrically conductive material, such that an outer cover 11 welded toa bottom surface 14 at the closed end of can 12 serves as an electricalcontact terminal for the cell.

Cell 10 further typically includes a first electrode material 15, whichmay serve as the positive electrode (also known as a cathode). The firstelectrode material 15 may be preformed and inserted into can 12, or maybe molded in place so as to contact the inner surfaces of the can 12.For an alkaline cell, first electrode material 15 will typically includeMnO2. After the first electrode 15 has been provided in can 12, aseparator 17 is inserted into the space defined by first electrode 15.Separator 17 is preferably a non-woven fabric. Separator 17 is providedto maintain a physical separation of the first electrode material 15 anda mixture of electrolyte and a second electrode material 20 whileallowing the transport of ions between the electrode materials.

Once separator 17 is in place within the cavity defined by firstelectrode 15, an electrolyte is dispensed into the space defined byseparator 17, along with the mixture 20 of electrolyte and a secondelectrode material, which may be the negative electrode (also known asthe anode). The electrolyte/second electrode mixture 20 preferablyincludes a gelling agent. For a typical alkaline cell, mixture 20 isformed of a mixture of an aqueous KOH electrolyte and zinc, which servesas the second electrode material. Water and additional additives mayalso be included in mixture 20.

Once the first electrode 15, separator 17, the electrolyte, and mixture20 have been formed inside can 12, a preassembled collector assembly 25is inserted into the open end of can 12. Can 12 is typically slightlytapered at its open end. This taper serves to support the collectorassembly in a desired orientation prior to securing it in place. Aftercollector assembly 25 has been inserted, an outer cover 45 is placedover collector assembly 25. Collector assembly 25 is secured in place byradially squeezing the can against collector assembly 25. The outercover 45 is then placed over and in contact with collector assembly 25.The end edge 13 of can 12 is then crimped over the peripheral lip ofcollector assembly 25, thereby securing outer cover 45 and collectorassembly 25 within the end of can 12. As described further below, onefunction served by collector assembly 25 is to provide for a secondexternal electrical contact for the electrochemical cell. Additionally,collector assembly 25 must seal the open end of can 12 to prevent theelectrochemical materials therein from leaking from this cell.Additionally, collector assembly 25 must exhibit sufficient strength towithstand the physical abuse to which batteries are typically exposed.Also, because electrochemical cells may produce hydrogen gas, collectorassembly 25 may allow internally-generated hydrogen gas to permeatetherethrough to escape to the exterior of the electrochemical cell.Further, collector assembly 25 should include some form of pressurerelief mechanism to relieve pressure produced internally within the cellshould this pressure become excessive. Such conditions may occur whenthe electrochemical cell internally generates hydrogen gas at a ratethat exceeds that at which the internally-generated hydrogen gas canpermeate through the collector assembly to the exterior of the cell.

The collector assembly 25 shown in FIG. 1 includes a seal 30, acollector nail 40, an inner cover 44, a washer 50, and a plurality ofspurs 52. Seal 30 is shown as including a central hub 32 having a holethrough which collector nail 40 is inserted. Seal 30 further includes aV-shaped portion 34 that may contact an upper surface 16 of firstelectrode 15.

Seal 30 also includes a peripheral upstanding wall 36 that extendsupward along the periphery of seal 30 in an annular fashion. Peripheralupstanding wall 36 not only serves as a seal between the interface ofcollector assembly 25 and can 12, but also serves as an electricalinsulator for preventing an electrical short from occurring between thepositive can and negative contact terminal of the cell.

Inner cover 44, which is formed of a rigid metal, is provided toincrease the rigidity and supports the radial compression of collectorassembly 25 thereby improving the sealing effectiveness. As shown inFIG. 1, inner cover 44 is configured to contact central hub portion 32and peripheral upstanding wall 36. By configuring collector assembly 25in this fashion, inner cover 44 serves to enable compression of centralhub portion 32 by collector nail 40 while also supporting compression ofperipheral upstanding wall 36 by the inner surface of can 12.

Outer cover 45 is typically made of a nickel-plated steel and isconfigured to extend from a region defined by the annular peripheralupstanding wall 36 of seal 30 and to be in electrical contact with ahead portion 42 of collector nail 40. Outer cover 45 may be welded tohead portion 42 of collector nail 40 to prevent any loss of contact. Asshown in FIG. 1, when collector assembly 25 is inserted into the openend of can 12, collector nail 40 penetrates deeply within theelectrolyte/second electrode mixture 20 to establish sufficientelectrical contact therewith. In the example shown in FIG. 1, outercover 45 includes a peripheral lip 47 that extends upwardly along thecircumference of outer cover 45. By forming peripheral upstanding wall36 of seal 30 of a length greater than that of peripheral lip 47, aportion of peripheral upstanding wall 36 may be folded over peripherallip 47 during the crimping process so as to prevent any portion of theupper edge 13 of can 12 from coming into contact with outer cover 45.

Seal 30 is preferably formed of nylon. In the configuration shown inFIG. 1, a pressure relief mechanism is provided for enabling the reliefof internal pressure when,such pressure becomes excessive. Further,inner cover 44 and outer cover 45 are typically provided with apertures43 that allow the hydrogen gas to escape to the exterior of cell 10. Themechanism shown includes an annular metal washer 50 and a plurality ofspurs 52 that are provided between seal 30 and inner cover 44. Theplurality of spurs 52 each include a pointed end 53 that is pressedagainst a thin intermediate portion 38 of seal 30. Spurs 52 are biasedagainst the lower inner surface of inner cover 44 such that when theinternal pressure of cell 10 increases and seal 30 consequently becomesdeformed by pressing upward toward inner cover 44, the pointed ends 53of spurs 52 penetrate through the thin intermediate portion 38 of seal30 thereby rupturing seal 30 and allowing the escape of theinternally-generated gas through apertures 43.

Although the above-described collector assembly 25 performs all the,above-noted desirable functions satisfactorily, as apparent from itscross-sectional profile, this particular collector assembly occupies asignificant amount of space within the interior of the cell 10. Becausethe exterior dimensions of the electrochemical cell are generally fixedby the American National Standards Institute (ANSI), the greater thespace occupied by the collector assembly, the less space that there isavailable within the cell for the electrochemical materials.Consequently, a reduction in the amount of electrochemical materialsthat may be provided within the cell results in a shorter service lifefor the cell. It is therefore desirable to maximize the interior volumewithin an electrochemical cell that is available for theelectrochemically active components.

It should be noted that the construction shown in FIG. 1 is but oneexample of a cell construction. Other collector assemblies exist thatmay have lower profiles and hence occupy less space within the cell.However, such collector assemblies typically achieve this reduction inoccupied volume at the expense of the sealing characteristics of thecollector assembly or the performance and reliability of the pressurerelief mechanism. It is therefore desirable to construct anelectrochemical cell where the space occupied by the collector assemblyand the space occupied by the container volume are minimized while stillmaintaining adequate sealing characteristics and a reliable pressurerelief mechanism.

The measured external and internal volumes for several batteries thatwere commercially available as of the filing date of this applicationare listed in the tables shown in FIGS. 2A and 2B. The tables list thevolumes (cc) for D, C, AA, and AAA sized batteries. Also provided inFIG. 2A is a percentage of the total cell volume that constitutes theinternal volume that is available for containing the electrochemicallyactive materials. The total cell volume includes all of the volume,including any internal void spaces, of the battery. For the batteryshown in FIG. 1, the total volume ideally includes all of thecross-hatched area as shown in FIG. 3A. The “internal volume” of thebattery is represented by the cross-hatched area shown in FIG. 3B. The“internal volume,” as used herein, is that volume inside the cell orbattery that contains the electrochemically active materials as well asany voids and chemically inert materials (other than the collector nail)that are confined within the sealed volume of the cell. Such chemicallyinert materials may include separators, conductors, and any inertadditives in the electrodes. As described herein, the term“electrochemically active materials” includes the positive and negativeelectrodes and the electrolyte.

The collector assembly volume includes the collector nail, seal, innercover, and any void volume between the bottom surface of the negativecover and the seal (indicated by the cross-hatched area in FIG. 3C). Itshould be appreciated that the sum total of the “internal volume,”“collector assembly volume,” and “container volume” is equal to thetotal volume. Accordingly, the internal volume available forelectrochemically active materials can be confirmed by measuring thecollector assembly volume and container volume and subtracting thecollector assembly volume and the container volume from the measuredtotal volume of the battery. The “container volume” includes the volumeof the can, label, negative cover, void volume between the label andnegative cover, positive cover, and void volume between the positivecover and can (shown by the cross-hatched area in FIG. 3D). If the labelextends onto and into contact with the negative cover, the void volumepresent between the label and negative cover is included in thecontainer volume, and therefore is also considered as part of the totalvolume. Otherwise, that void volume is not included in either of thecontainer volume or the total volume. The collector assembly volume andthe percentage of the total cell volume that constitutes the collectorassembly volume is provided in FIG. 2B for those commercially availablebatteries listed in FIG. 2A.

The total battery volume, collector assembly volume, and internal volumeavailable for electrochemically active material for each battery aredetermined by viewing a Computer Aided Design (CAD) drawing, aphotograph, or an actual cross section of the battery which has beenencased in epoxy and longitudinally cross-sectioned. The use of a CADdrawing, photograph, or actual longitudinal cross section to view andmeasure battery dimensions allows for inclusion of all void volumes thatmight be present in the battery. To measure the total battery volume,the cross-sectional view of the battery taken through its centrallongitudinal axis of symmetry is viewed and the entire volume ismeasured by geometric computation. To measure the internal volumeavailable for electrochemically active materials, the cross-sectionalview of the battery taken through its central longitudinal axis ofsymmetry is viewed, and the components making up the internal volume,which includes the electrochemically active materials, void volumes andchemically inert materials (other than the collector nail) that areconfined within the sealed volume of the cell, are measured by geometriccomputation. Likewise, to determine volume of the collector assembly,the cross-sectional view of the battery taken through its centrallongitudinal axis of symmetry thereof is viewed, and the componentsmaking up the collector assembly volume, which include the collectornail, seal, inner cover, and any void volume defined between the bottomsurface of the negative cover and the seal, are measured by geometriccomputation. The container volume may likewise be measured by viewingthe central longitudinal cross section of the battery and computing thevolume consumed by the can, label, negative cover, void volume betweenthe label and negative cover, positive cover, and void volume betweenthe positive cover and the can.

The volume measurements are made by viewing a cross section of thebattery taken through its longitudinal axis of symmetry. This providesfor an accurate volume measurement, since the battery and its componentsare usually axial symmetric. To obtain a geometric view of the crosssection of a battery, the battery was first potted in epoxy and, afterthe epoxy solidified, the potted battery and its components were grounddown to the central cross section through the axis of symmetry. Moreparticularly, the battery was first potted in epoxy and then groundshort of the central cross section. Next, all internal components suchas the anode, cathode, and separator paper were removed in order tobetter enable measurement of the finished cross section. The pottedbattery was then cleaned of any remaining debris, was air dried, and theremaining void volumes were filled with epoxy to give the battery someintegrity before completing the grinding and polishing to its center.The battery was again ground and polished until finished to its centralcross section, was thereafter traced into a drawing, and the volumesmeasured therefrom.

Prior to potting the battery in epoxy, battery measurements were takenwith calipers to measure the overall height, the crimp height, and theoutside diameter at the top, bottom, and center of the battery. Inaddition, an identical battery was disassembled and the componentsthereof were measured. These measurements of components of thedisassembled battery include the diameter of the current collector nail,the length of the current collector nail, the length of the currentcollector nail to the negative cover, and the outside diameter of thetop, bottom, and center of the battery without the label present.

Once the battery was completely potted in epoxy and ground to centerthrough the longitudinal axis of symmetry, the cross-sectional view ofthe battery was used to make a drawing. A Mitutoyo optical comparitorwith QC-4000 software was used to trace the contour of the battery andits individual components to generate a drawing of the central crosssection of the battery. In doing so, the battery was securely fixed inplace and the contour of the battery parts were saved in a format thatcould later be used in solid modeling software to calculate the batteryvolumes of interest. However, before any volume measurements were taken,the drawing may be adjusted to compensate for any battery componentsthat are not aligned exactly through the center of the battery. This maybe accomplished by using the measurements that were taken from thebattery before cross sectioning the battery and those measurements takenfrom the disassembled identical battery. For example, the diameter andlength of the current collector nail, and overall outside diameter ofthe battery can be modified to profile the drawing more accurately byadjusting the drawing to include the corresponding known cross-sectionaldimensions to make the drawing more accurate for volume measurements.The detail of the seal, cover, and crimp areas were used as they weredrawn on the optical comparitor.

To calculate the volume measurements, the drawing was imported intosolid modeling software. A solid three-dimensional volume representationwas generated by rotating the contour of the cross section on both theleft and right sides by one-hundred-eighty degrees (180°) about thelongitudinal axis of symmetry. Accordingly, the volume of each region ofinterest is calculated by the software and, by rotating the left andright sides by one-hundred-eighty degrees (180°) and summing the leftand right volumes together an average volume value is determined, whichmay be advantageous in those situations where the battery hasnon-symmetrical features. The volumes which include any non-symmetricalfeatures can be adjusted as necessary to obtain more accurate volumemeasurements.

SUMMARY OF THE INVENTION

Accordingly, it is an aspect of the present invention to solve the aboveproblems by either eliminating the collector assembly from the cellwhile retaining its functions, or by providing a collector assemblyhaving a significantly lower profile and thereby occupying significantlyless space within an electrochemical cell. Another aspect of the presentinvention is to provide cell constructions exhibiting lower water lossover time than prior assemblies, thereby increasing the cell's shelflife. An additional aspect of the invention is to provide a batteryhaving a reliable pressure relief mechanism that does not occupy asignificant percentage of the available cell volume. Still yet anotheraspect of the present invention is to provide cell constructions thatare simpler to manufacture and that require less materials, therebypossibly having lower manufacturing costs. Another aspect of theinvention is to provide cell constructions that require less radialcompressive force to be applied by the can to adequately seal the cell,thereby allowing for the use of a can having thinner side walls, andthus resulting in greater internal cell volume.

To achieve some of these and other aspects and advantages, a battery ofthe present invention comprises a can for containing electrochemicalmaterials including positive and negative electrodes and an electrolyte,the can having a first end, an open second end, side walls extendingbetween the first and second ends, and an end wall extending across thefirst end; a pressure relief mechanism formed in the end wall of the canfor releasing internal pressure from within the can when the internalpressure becomes excessive; a first outer cover positioned on the endwall of the can to be in electrical contact therewith and to extend overthe pressure relief mechanism; a second outer cover positioned acrossthe open second end of the can; and an insulator disposed between thecan and the second outer cover for electrically insulating the can fromthe second outer cover.

Additionally, some of the above aspects and advantages may be achievedby a battery of the present invention that comprises a can forcontaining electrochemically active materials including at leastpositive and negative electrodes and an electrolyte, the can having afirst end, an open second end, side walls extending between the firstand second ends, and an end wall extending across the first end, the canfurther having a flange that extends outward from the open second end ofthe can towards the first end; a cover for sealing the open end of thecan, the cover having a peripheral edge that extends over and around theflange and is crimped between the flange and an exterior surface of theside walls of the can; and electrical insulation provided between theflange and the peripheral edge of the cover and between the can and theperipheral edge. The electrical insulating material is preferablyprovided in the form of a coating deposited directly on at least one ofthe can and the outer cover.

Further, some of the above aspects and advantages may also be achievedby an electrochemical cell of the present invention that comprises a canfor containing electrochemically active materials including at leastpositive and negative electrodes and an electrolyte, the can having anopen end and a closed end, and side walls extending between the open endand closed end; a first outer cover positioned across the open end ofthe can; a collector electrically coupled to the first outer cover andextending internally within the can to electrically contact one of thepositive and negative electrodes; and an annular seal having an L-shapedcross section disposed between the can and the first outer cover forelectrically insulating the can from the first outer cover and creatinga seal between the first outer cover and the can. The seal may furtherinclude an extended vertical member to form a J-shaped cross section.According to this embodiment, a pressure relief mechanism is preferablyformed in a surface of the can for releasing internal pressure fromwithin the can when the internal pressure becomes excessive.

Yet, some of the above aspects and advantages may be achieved by anelectrochemical cell of the present invention that comprises a can forcontaining electrochemically active materials including at leastpositive and negative electrodes and an electrolyte, the can having anopen end, a closed end, and side walls extending between the open andclosed ends; a cover positioned across the open end of the can andconnected to the can, the cover having an aperture extendingtherethrough; a current collector extending through the aperture in thecover and extending internally within the can to electrically contactone of the positive and negative electrodes; and an insulating materialdisposed between the collector and the cover for electrically insulatingthe collector from the cover and creating a seal between the collectorand the cover. In addition, the electrochemical cell preferably includesa first contact terminal electrically coupled to the collector and adielectric material disposed between the first contact terminal and thecover for electrically insulating the cover from the first contactterminal. Also provided is a method of manufacturing an electrochemicalcell which includes the steps of dispensing active electrochemicalmaterials in a can having a closed end and an open end; disposing acollector through an aperture formed in a cover; providing a dielectricinsulating material between the cover and the collector to provideelectrical insulation therebetween; and assembling the cover andcollector to the open end of the can.

Further, some of the above aspects and advantages may also be achievedby a battery of the present invention that comprises a can forcontaining electrochemically active materials including positive andnegative electrodes and an electrolyte, and a label printed directly onan exterior surface of the can. A method of assembling a battery is alsoprovided including the steps of forming a can having an open end and aclosed end, forming an outer cover, dispensing electrochemically activematerials in the can, sealing the outer cover across the open end of thecan with a layer of electrical insulation provided therebetween, andprinting a label directly on the exterior surface of the can. Accordingto this embodiment, the diameter of the can may be correspondinglyincreased to allow a significant increase in the internal volume of thebattery, while maintaining a predetermined total outside diameter.

These and other features, advantages, and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims, andappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a cross section of a conventional C sized alkalineelectrochemical cell;

FIG. 2A is a table showing the relative total battery volumes andinternal cell volumes available for electrochemically active materials,as measured for those batteries that were commercially available at thetime this application was filed;

FIG. 2B is a table showing the relative total battery volumes andcollector assembly volumes as measured for those batteries that werecommercially available as provided in FIG. 2A;

FIGS. 3A-3D are cross sections of a conventional C sized alkalineelectrochemical cell that illustrate the total battery and variouscomponent volumes;

FIG. 4 is a cross section of a C sized alkaline electrochemical cellhaving a low profile seal constructed in accordance with a firstembodiment of the present invention;

FIG. 5 is a partial cross section of an adaption of the first embodimentfor use in an AA sized battery shown in comparison with a partial crosssection of an adaptation of the conventional construction as currentlyused in an AA sized battery;

FIG. 6 is a cross section of a C sized alkaline electrochemical cellhaving an ultra low profile seal according to a second embodiment of thepresent invention;

FIG. 7 is a cross section of a C sized alkaline electrochemical cellhaving an ultra low profile seal and a formed positive cover protrusionaccording to a third embodiment of the present invention;

FIG. 8A is a cross section of a C sized alkaline electrochemical cellconstructed in accordance with a fourth embodiment of the presentinvention having a rollback cover, an annular L-shaped or J-shaped seal,and a pressure relief mechanism formed in the can bottom surface;

FIG. 8B is a cross section of the top portion of a C sized alkalineelectrochemical cell constructed in accordance with the fourthembodiment of the present invention having a rollback cover and furtherincluding an L-shaped annular seal;

FIG. 8C is an exploded perspective view of the electrochemical cellshown in FIG. 8A illustrating assembly of the collector seal and coverassembly;

FIG. 9 is a bottom view of a battery can having a pressure reliefmechanism formed in the closed end of the can;

FIG. 10 is a cross-sectional view taken along line X—X of the can ventshown in FIG. 9;

FIG. 11 is a cross section of a C sized alkaline electrochemical cellhaving a beverage can-type construction according to a fifth embodimentof the present invention;

FIG. 12A is a partially exploded perspective view of the battery shownin FIG. 11;

FIGS. 12B and 12C are cross-sectional views of a portion of the batteryshown in FIG. 11 illustrating the process for forming the beveragecan-type construction;

FIG. 12D is an enlarged cross-sectional view of a portion of the batteryshown in FIG. 11;

FIG. 13 is a cross section of a C sized alkaline electrochemical cellhaving a beverage can-type construction according to a sixth embodimentof the present invention;

FIG. 14A is a table showing the calculated total and internal cellvolume for various batteries constructed in accordance with the presentinvention;

FIG. 14B is a table showing the calculated total volume and collectorassembly volume for various batteries constructed in accordance with thepresent invention;

FIG. 15 is a cross section of a C sized alkaline electrochemical cellhaving a collector feed through construction according to a seventhembodiment of the present invention;

FIG. 16 is an exploded assembly view of the electrochemical cell shownin FIG. 15; and

FIG. 17 is a flow diagram illustrating a method of assembly of theelectrochemical cell shown in FIGS. 15 and 16.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As described above, a primary objective of the present invention is toincrease the internal volume available in a battery for containing theelectrochemically active materials to volumes previously not obtained.To achieve this objective without detrimentally decreasing thereliability of the pressure relief mechanism provided in the battery andwithout increasing the likelihood that the battery would otherwise leak,various novel modifications are suggested below to the construction ofbatteries of various sizes. The modifications described below may beimplemented separately or in combination in a battery to improve itsvolume efficiency.

As described in further detail below, the various modifications of thepresent invention that achieve greater internal volume for containingthe electrochemically active materials, include a low profile seal (FIG.4), an ultra low profile seal (FIG. 5), a positive outer coverprotrusion formed directly in the closed end of the can used incombination with the ultra low profile seal (FIG. 6) or the low profileseal, a can vent formed in the closed end of the battery can (FIGS. 7-9)including an L-shaped and J-shaped annular seal (FIGS. 8A-8C), abeverage can-type construction used in combination with a can vent (FIG.11), and a beverage can-type construction with a collector feed through(FIGS. 15-17).

Additionally, through the use of the constructions noted above, thebattery can may be made with thinner walls, on the order of 4-8 mils,since the construction techniques outlined below do not require thethicker walls that are required in conventional batteries to ensure asufficient crimp and seal. Further, in accordance with the presentinvention, a label may be lithographed directly onto the exteriorsurface of the battery can. By making the can walls thinner andlithographing the label directly onto the exterior of the can, theinternal volume of the cell may be further increased since one does nothave to account for the thickness of the label substrate to construct acell that meets the ANSI exterior size standards.

Low Profile Seal

FIG. 4 shows a battery constructed using a low profile seal inaccordance with a first embodiment of the present invention. Similar tothe battery shown in FIG. 1, battery 100 includes an electricallyconductive can 112 having a closed end 114 and an open end in which acollector assembly 125 and negative cover 145 are secured in place.Also, battery 100 includes a positive electrode 115 in contact with theinterior walls of can 112 and in contact with a separator layer 117 thatlies between positive electrode 115 and a negative electrode 120.Further, battery 100 includes a positive outer cover 111 attached to abottom surface of the closed end of can 112.

The difference between batteries 10 and 100 lies in the construction ofcollector assembly 125 and cover 145. While seal 130 is similar to seal30 in that it includes an upstanding wall 136 and a central hub 132,which has an aperture formed therein for receiving the head portion 142of a collector nail 140, seal 130 differs from seal 30 in that the Vportion 34 of seal 30 is inverted to extend upward toward inner cover144, as indicated by reference numeral 134. By inverting this V portion,collector assembly 125 may rest more squarely upon an upper surface 116of positive electrode 115. Further, the volume occupied by the V portion34 of battery 10 may then be used for the electrochemically activematerials.

To also reduce the internal volume occupied by collector assembly 125,inner cover 144 is constructed to more closely conform to the innersurface of outer cover 145 so as to eliminate the void space betweenouter cover 45 and inner cover 44 in battery 10. Additionally, byresting collector assembly 125 firmly on top surface 116 of positiveelectrode 115, the peripheral edge 147 of outer cover 145 may be flatrather than extend upward, as in the case for battery 10. By layingperipheral edge 147 flat, collector assembly 125 may be positioned evencloser to the end of battery 100.

Collector assembly 125 of battery 100 further differs from collectorassembly 25 of battery 10 in that spurs 52 and washer 50 are eliminated.Collector assembly 125, nevertheless, has a reliable pressure reliefmechanism by the provision of a thinned-out section 138 formed in seal130 immediately adjacent hub 132. A thickened ring portion 139 of seal130 is provided adjacent thinned-out portion 138 such that thinned-outportion 138 lies between thickened ring portion 139 and the relativelythick hub 132. Thus, when the internal pressure of cell 100 becomesexcessive, seal 130 rips open in the location of thinned-out portion138. As with the construction shown for battery 10, theinternally-generated gas then escapes through apertures 143 formed ininner cover 144 and outer cover 145.

The internal volume available for containing electrochemically activematerials in a D sized battery having the conventional constructionshown in FIG. 1, is 44.16 cc, which is 87.7 percent of the total volumeof 50.38 cc. (See the corresponding entry in the table of FIG. 2A.) Ifthe same cell were constructed using the low profile seal constructionshown in FIG. 4, the internal cell volume may be increased to 44.67 cc,which represents 89.2 percent of the total volume, which is 50.07 cc.The internal and external volumes for the cell constructed with the lowprofile seal of the present invention are for a cell having a 10 mil canthickness. Further, by decreasing the can wall thickness, even greaterinternal cell volumes may be achieved.

The low profile seal described above is disclosed in commonly-assignedU.S. patent application Ser. No. 08/882,572 entitled “A V-SHAPED GASKETFOR GALVANIC CELLS,” filed on Jun. 27, 1997, by Gary R. Tucholski, thedisclosure of which is incorporated by reference herein.

FIG. 5 shows a modified adaptation of the low profile seal as used in anAA sized battery 100′ in comparison with a commercial adaptation of theconstruction shown in FIG. 1 as used for an AA sized battery 10′. Likethe collector assembly of battery 100 (FIG. 4), the collector assemblyof battery 100′ includes a seal 130 having an inverted-V portion 134, ahub portion 132, and a thinned-out portion 138 provided between hub 132and a thickened portion 139.

The primary difference between the collector assemblies of batteries 100and 100′ is the elimination of inner cover 144 of battery 100. To ensuresufficient radial compressive force against upstanding leg 136 of seal130, battery 100′ uses a rollback cover 145′ in place of the flangedcover 145 used in battery 100 and also utilizes a retainer 150. As willbe apparent from a comparison of FIGS. 4 and 5, a rollback cover differsfrom a flanged cover in that the peripheral edge 147 of a flanged cover145 is flat whereas the peripheral edge 147′ of a rollback cover 145′extends axially downward and is folded to also extend axially upward.Rollback cover 145′ provides a sufficient spring force in the radialdirection to maintain compression of upstanding leg 136 of seal 130against the inner wall of can 112 during normal use.

Retainer 150 is provided over and around the upper portion of hub 132 ofseal 130 to compress hub 132 against collector nail 140. Also, byconfiguring retainer 150 to have a J- or L-shaped cross section, thelower radial extension of retainer 150 can ensure that seal 130 willrupture in the vicinity of thinned-out portion 138 when the internalpressure reaches an excessive level.

Ultra Low Profile Seal

FIG. 6 shows a battery constructed in accordance with a secondembodiment of the present invention, which utilizes an ultra low profileseal. Like the conventional cell 10 shown in FIG. 1, cell 200 alsoincludes a cylindrical can 212 made of an electrically conductivematerial. Also, a first electrode 215 is formed against the inner wallsof can 212 preferably by molding. A separator 217 is likewise insertedwithin the cavity defined by first electrode material 215, and a mixture220 of a second electrode and electrolyte are provided within a cavitydefined by the separator 217.

As shown in FIG. 6, collector assembly 225 includes an integralseal/inner cover assembly 228 and a collector 240 that passes through acentral hole 236 provided in the integral seal/inner cover assembly 228.Collector 240 is preferably a brass nail including a head 242 and aretainer flange 241 that is provided to cooperate with a speed nut 250to secure collector nail 240 within central hole 236 of integratedseal/inner cover assembly 228.

Integrated seal/inner cover assembly 228 includes a rigid inner cover210 and a seal 230 that is formed directly on rigid inner cover 210 bymolding or lamination. Seal 230 is preferably made of neoprene, butyl,or ethylene propylene rubber, and rigid inner cover 210 is preferablyformed of low-carbon steel 1008 or 1010. Because rubber is morecompressible than the nylon or polypropylene materials often used insuch collector assemblies, the radial compressive strength of the rigidinner cover 210 need not be as great. Thus, the inner cover could bemade of thinner and/or softer metals. Further, materials other thanmetal may be used. Also, seal 230 may be formed of other materialsprovided such materials are chemically inert, water impervious,compressible, and exhibit the ability to bond to the material used toform rigid inner cover 210.

Additionally, by decreasing the radial force required to compress theperipheral upstanding wall of the seal, the thickness of the can wallsmay be decreased from 0.010 inch (10 mils) to approximately 0.006 (6mils) or possibly even 0.004 inch (4 mils).

By providing a structure that enables rubber materials such as neopreneand butyl rubber to be used as the seal material, the water permeabilityof the collector assembly is significantly reduced. By reducing thewater permeability of the cell, the service maintenance of the batteryshould be increased.

Rigid inner cover 210 is generally disk shaped and has a centralaperture 218 formed at its center as well as a plurality of additionalapertures 217. Central aperture 218 and additional apertures 217 extendthrough rigid inner cover 210 from its upper surface to its bottomsurface. If formed of metal, rigid inner cover 210 is preferablyproduced by stamping it from a sheet of metal. Inner cover 210 may,however, be formed using other known manufacturing techniques.Subsequently, rigid inner cover 210 may be subjected to a surfaceroughening process, such as sandblasting or chemical etching, to enhancethe strength of the bond that is subsequently formed between rigid innercover 210 and seal 230. For a C sized cell, rigid inner cover 210 ispreferably 0.015 to 0.030 inch thick.

After rigid inner cover 210 has been stamped and surface treated, it ispreferably inserted into a transfer mold press into which the rubberthat forms seal 230 is subsequently supplied. The transfer mold ispreferably formed to allow the supplied rubber to form a layer 232across the bottom surface of rigid inner cover 210. The thickness oflayer 232 is between 0.010 and 0.020 inch thick, and is preferably about0.016 inch thick. The rubber also flows into apertures 217 to form plugs238. Also, the rubber flows within central aperture 218 so as to linethe surfaces of central aperture 218 but without completely filling theaperture so as to provide a central hole 236 into which collector nail240 may subsequently be inserted. The diameter of central hole 236 ispreferably sufficiently smaller than the diameter of collector nail 240such that the rubber lining in central aperture 218 is significantlycompressed within aperture 218 when collector nail 240 is driven inplace through central hole 236. By providing a retainer 241 on collector240 that is pressed against bottom layer 232 of seal 230, when collectornail 240 has been driven in place, its speed nut 250 and retainer 241cooperate to also vertically compress the portion of rubber layer 232lying therebetween. By compressing the rubber seal in the vicinity ofcollector nail 240 in this manner, the possibility of a leak occurringin the interface between the collector nail 240 and integratedseal/inner cover assembly 228 is significantly reduced.

By filling apertures 217 with rubber seal plugs 238 in the manner shown,a pressure relief mechanism is provided that not only works reliably,but which may effectively reseal after internal pressure has beenreleased. When the internal pressure reaches levels considered to beexcessive, the excessive pressure ruptures at least one of plugs 238 toallow the expedited release of internally-generated gasses. The pressureat which such rupturing occurs is controllable based upon the materialsselected for the seal, the thickness of the seal material, and thediameter of apertures 217. Further, because of the elasticity of therubber seal material, the rubber plug 238 substantially assumes itsoriginal state once the pressure has been released. Thus, unlike otherventing mechanisms used in conventional collector assemblies, thepressure relief mechanism of the present invention does not create apermanent hole within the collector assembly through whichelectrochemical materials may subsequently leak. Also, such resealingminimizes deterioration of the cell's internal components, therebypossibly extending the useful cell life.

Although only one aperture 217 in plug 238 need be provided to serve asa pressure relief mechanism, added reliability is obtained by providinga plurality of such plugged apertures. Unlike prior art relief mechanismstructures, the present invention allows for a plurality ofindependently-operable pressure relief mechanisms. Even the pressurerelief mechanism illustrated in FIG. 1, which includes a plurality ofspurs, relies upon the inversion of washer 50 for any one of the spursto penetrate the seal. Each of the plugged apertures provided in thecollector assembly of the present invention, however, is not dependentupon one another, and therefore provide for a more reliable pressurerelief mechanism as a whole.

As shown in FIG. 6, seal 230 has an upstanding wall 235 formed directlyon a peripheral edge of rigid inner cover 210. By providing thisupstanding wall 235, a sufficient seal may be created when collectorassembly 225 is inserted into can 212. This seal is further enhanced byforming the outer diameter of seal 230 to be greater than the insidediameter of can 212 so that inner cover 210 compresses upstanding wall235 against the inner surface of can 212.

Seal 230 may additionally be formed to include an extended portion 237of upstanding wall 235 that extends vertically upward past the uppersurface of inner cover 210. By providing extension 237, seal 230 may beused as an electrical insulator between the crimped end 224 of can 212and a peripheral edge of outer cover 245.

Although seal 230 is shown as including a continuous layer 232 acrossthe entire bottom surface of inner cover 210, it will be appreciated bythose skilled in the art that seal 230 need not be formed over theentire bottom surface of inner cover 210, particularly if inner cover210 is formed of an inert plastic material. Depending upon thecharacteristics of the materials used to form seal 230 and inner cover210, a bonding agent may be applied to the surfaces of inner cover 210that will come into contact and be bonded to seal material 230.

Once seal 230 has been molded to inner cover 210 and collector nail 240is inserted through central hole 236 of integrated seal/inner coverassembly 228 and through retainer 240, outer cover 245 is placed on theupper surface of collector assembly 225 and is preferably welded to head242 of collector nail 240. Subsequently, the collector assembly 225 withthe outer cover 245 attached thereto is inserted into the open end ofcell can 212. To hold collector assembly 225 in place prior to crimping,the bottom surface of collector assembly 225 is rested upon an uppersurface 216 of first electrode 215. Thus, collector assembly 225 may beinserted with some degree of force to ensure that the bottom layer 232of seal 230 rests evenly within the cell can opening on upper surface216 of electrode 215.

If first electrode 215 is formed by molding it in place within can 212,first electrode 215 is preferably constructed in the manner disclosed incommonly-assigned U.S. patent application Ser. No. 09/036,115 entitled“ELECTROCHEMICAL CELL STRUCTURE EMPLOYING ELECTRODE SUPPORT FOR THESEAL,” filed on Mar. 6, 1998, by Gary R. Tucholski et al. to prevent anyflashing resulting from the molding of first electrode 215 frominterfering with the proper alignment and seal provided by the collectorassembly. The disclosure of U.S. patent application Ser. No. 09/036,115is incorporated by reference herein.

By resting collector assembly 225 on electrode 215, can 212 could becrimped at its open end so as to provide a downward force that iscountered by electrode 215. Thus, the higher profile crimp used in theconventional cell construction shown in FIG. 1 may be replaced with alower profile crimp, thereby creating about 0.060 inch more space insidethe cell.

A collector assembly 225 having the construction shown in FIG. 6 has amuch lower profile than the conventional collector assembly asillustrated in FIG. 1. Thus, a cell 200 utilizing collector assembly 225may include greater amounts of electrochemical materials 215 and 220,and the service life of the cell is increased accordingly. Despite itslower profile, collector assembly 225 nevertheless exhibits sufficientsealing and electrical insulation. Additionally, the collector assemblyof the present invention provides a pressure relief mechanism that isnot only reliable, but which provides the advantages of multipleindependently-operable pressure relief mechanisms and partial resealingafter venting to prevent the subsequent leakage of electrochemicalmaterials from the cell. Further, the collector assembly of the presentinvention offers improved water permeability characteristics, therebyincreasing the service maintenance of the battery.

The calculated total volumes (cc) and internal volumes (cc) availablefor containing electrochemically active materials for batteries ofvarious sizes constructed using the ultra low profile seal shown in FIG.6, are provided in the table shown in FIG. 14A. As apparent from thetable in FIG. 14A, the internal cell volumes for such cells aregenerally greater than any of the prior commercially-available cells.For example, a D sized battery employing the ultra low profile seal hasan internal volume available for containing electrochemically activematerials of 45.53 cc, which is 90.9 percent of the total volume of50.07 cc. This is greater than the internal volume measured on any ofthe conventional cells listed in FIG. 2A. Further, for cells having acan thickness of 8 mils or 6 mils, the internal cell volume may befurther significantly increased. The calculated total volumes (cc) arefurther shown in the table presented in FIG. 14B, in comparison with thecollector assembly volumes for batteries of various sizes constructedusing the ultra low profile seal shown in FIG. 6. The collector assemblyvolume as defined herein includes the collector nail, seal, inner cover,and any void volume between the bottom surface of the negative cover andthe seal. The container volume as defined herein includes the volumeused by the can, label, negative cover, void volume between the labeland the negative cover, positive cover, and the void volume between thepositive cover and can. It should be appreciated that the total volumeof the battery is equal to the summation of the internal volumeavailable for electrochemically active materials, the collector assemblyvolume, and the container volume. The total volume of the battery,collector assembly volume and container volume are determined by viewinga CAD drawing of the central longitudinal cross-sectional view of thebattery. As is apparent from the table in FIG. 14B, the collectorassembly volume is generally less than any of the priorcommercially-available cells. It should be appreciated that thecollector assembly volume is decreased by using the ultra low profileseal construction. For example, the collector assembly volume consumedin the ultra low profile seal is 1.89 cc, which is 3.8 percent of thetotal volume of 50.07 cc as shown in FIG. 14B. In contrast, this is lessthan any of the collector assembly volumes measured from theconventional batteries as listed in FIG. 2B. The container volume mayalso be decreased. Similarly, for cells having a reduced can thicknessof 8 mils or 6 mils, the internal cell volume may be furthersignificantly increased, while the container volume is decreased.

The ultra low profile seal described above, and several alternativeembodiments of the ultra low profile seal, are disclosed incommonly-assigned U.S. patent application Ser. No. 09/036,208 entitled“COLLECTOR ASSEMBLY FOR AN ELECTROCHEMICAL CELL INCLUDING AN INTEGRALSEAL/INNER COVER,” filed on Mar. 6, 1998, by Gary R. Tucholski, thedisclosure of which is incorporated by reference herein.

Low Profile Seal and Ultra Low Profile Seal With Formed PositiveProtrusion

As shown in FIG. 7, the second embodiment shown in FIG. 6 may bemodified to have the protrusion 270 for the positive battery terminalformed directly in the closed end 214′ of can 212. In this manner, thevoid space existing between the closed end 214 of can 212 and positiveouter cover 211 (FIG. 6) may be used to contain electrochemically activematerials or otherwise provide space for the collection of gasses, whichotherwise must be provided within the cell. It will further beappreciated by those skilled in the art that the first embodiment shownin FIG. 4 may similarly be modified, such that the positive outer coverprotrusion is formed directly in the bottom of can 112. Although theincrease in cell volume obtained by forming the protrusion directly inthe bottom of the can is not provided in the table in FIG. 14A, it willbe appreciated by those skilled in the art that the internal volume istypically one percent greater than the volumes listed for the ultra lowprofile seal or low profile seal listed in the table, which are formedwith a separate cover.

Pressure Relief Mechanism Formed in Can Bottom with L-Shaped Seal

An electrochemical battery 300 constructed in accordance with a fourthembodiment of the present invention is shown in FIGS. 8A through 8C.Battery 300 differs from the prior battery constructions in that apressure relief mechanism 370 is formed in the closed end 314 of can312. As a result, complex collector/seal assemblies may be replaced withcollector assemblies that consume less volume and have fewer parts.Thus, a significant improvement in internal cell volume efficiency maybe obtained. As shown in FIGS. 8A, 8B, 9, and 10, the pressure reliefmechanism 370 is formed by providing a groove 372 in the bottom surfaceof can 312. This groove may be formed by coining a bottom surface of can312, cutting a groove in the bottom surface, or molding the groove inthe bottom surface of the can at the time the positive electrode ismolded. For an AA sized battery, the thickness of the metal at thebottom of the coined groove is approximately 2 mils. For a D sizedbattery, the thickness of the metal at the bottom of the coined grooveis approximately 3 mils. The groove may be formed as an arc ofapproximately 300 degrees. By keeping the shape formed by the grooveslightly open, the pressure relief mechanism will have an effectivehinge.

The size of the area circumscribed by the groove 372 is preferablyselected such that upon rupture due to excessive internal pressure, thearea within the groove 372 may pivot at the hinge within the positiveprotrusion of outer cover 311 without interference from outer cover 311.In general, the size of the area defined by the groove 372, as well asthe selected depth of the groove, depends upon the diameter of the canand the pressure at which the pressure relief mechanism is to ruptureand allow internally-generated gasses to escape.

Unlike pressure relief mechanisms that have been described in the priorart as being formed in the side or end of the can, the pressure reliefmechanism 370 of the present invention is positioned beneath outer cover311 so as to prevent the electrochemical materials from dangerouslyspraying directly outward from the battery upon rupture. Also, if thebattery were used in series with another battery such that the end ofthe positive terminal of the battery is pressed against the negativeterminal of another battery, the provision of outer cover 311 overpressure relief mechanism 370 allows mechanism 370 to bow outwardlyunder the positive protrusion and ultimately rupture. If outer cover 311was not present in such circumstances, the contact between the twobatteries may otherwise prevent the pressure relief mechanism fromrupturing. Further, if outer cover 311 were not provided over pressurerelief mechanism 370, the pressure relief mechanism at the positive endof the battery would be more susceptible to damage. Outer cover 311 alsoshields pressure relief mechanism 370 from the corrosive effects of theambient environment and therefore reduces the possibility of prematureventing and/or leaking. Thus, by forming the pressure relief mechanismunder the outer cover, the present invention overcomes the problemsassociated with the prior art constructions, and thus represents acommercially feasible pressure relief mechanism for a battery.

Because the formation of a pressure relief mechanism in the bottomsurface of a battery can eliminates the need for a complexcollector/seal assembly, the open end of the battery can may be sealedusing construction techniques that were not previously feasible due tothe need to allow gasses to escape through the pressure relief mechanismto the exterior of the battery. For example, as shown in FIGS. 8A and8B, the open end of can 312 may be sealed by placing either a nylon seal330 having a J-shaped cross section or a nylon seal 330′ having anL-shaped cross section in the open end of can 312, inserting a negativeouter cover 345 having a rolled back peripheral edge 347 within nylonseal 330 or 330′, and subsequently crimping the outer edge 313 of can312 to hold seal 330 or 330′ and cover 345 in place. To help hold seal330 or 330′ in place, a bead 316 may be formed around the circumferenceof the open end of can 312. Nylon seal 330 or 330′ may be coated withasphalt to protect it from the electrochemically active materials and toprovide a better seal.

Referring particularly to FIGS. 8A and 8C, the annular nylon seal 330 isshown configured with a J-shaped cross section which includes anextended vertical wall 332 at the outermost perimeter thereof, a shortervertical wall 336 at the radially inward side of the seal and has ahorizontal base member 334 formed between the vertical walls 332 and336. With the presence of the short vertical section 336, the annularseal is referred to herein as having either a J-shaped or L-shaped crosssection. It should be appreciated that the J-shaped nylon seal 330 couldalso be configured absent the short vertical section 336 to form a plainL-shaped cross section as shown in FIG. 8B.

With particular reference to FIG. 8C, the assembly of theelectrochemical cell shown in FIG. 8A is illustrated therein. Thecylindrical can 312 is formed with side walls defining the open end andbead 316 for receiving internally disposed battery materials prior toclosure of the can. Disposed within can 312 are the activeelectrochemical cell materials including the positive and negativeelectrodes and the electrolyte, as well as the separator, and anyadditives. Together, the outer cover 345, with the collector nail 340welded or otherwise fastened to the bottom surface of cover 345, andannular nylon seal 330 are assembled and inserted into the open end ofcan 312 to seal and close can 312. The collector nail 340 is preferablywelded via spot weld 342 to the bottom side of outer cover 345.Together, collector nail 340 and cover 345 are engaged with seal 330 toform the collector assembly, and the collector assembly is inserted incan 312 such that the rolled back peripheral edge 347 of outer cover 345is disposed against the inside wall of annular seal 330 above bead 316which supports seal 330. The collector assembly is forcibly disposedwithin the open end of can 312 to snuggly engage and close the canopening. Thereafter, the outer edge 313 of can 12 is crimped inward toaxially force and hold seal 330 and outer cover 345 in place.

Referring back to FIG. 8B, the inside surface of outer cover 345 and atleast a top portion of collector nail 340 are further shown coated withan anti-corrosion coating 344. Anti-corrosion coating 344 includesmaterials that are electrochemically compatible with the anode. Examplesof such electrochemically compatible materials include epoxy, Teflon®,polyolefins, nylon, elastomeric materials, or any other inert materials,either alone or in combination with other materials. Coating 344 may besprayed or painted on and preferably covers that portion of the insidesurface of outer cover 345 and collector nail 340 which is exposed tothe active materials in the void region above the positive and negativeelectrodes of the cell. It should also be appreciated that the insidesurface of cover 345 could be plated with tin, copper, or othersimilarly electrochemically compatible materials. By providing theanti-corrosion coating 344, any corrosion of the outer cover 345 andcollector nail 340 is reduced and/or prevented, which advantageouslyreduces the amount of gassing which may otherwise occur within theelectrochemical cell. Reduction in gassing within the cell results inreduced internal pressure buildup.

As shown in FIG. 14A in the rows referenced “Pressure Relief in CanBottom” and “Pressure Relief in Can Bottom With Thin Walls,” a D sizedbattery constructed using the construction shown in FIG. 8A, has aninternal volume that is 93.5 volume percent when the can walls are 10mils thick, and an internal volume that is 94.9 volume percent when thecan walls are 8 mils thick. As shown in FIG. 14B, a D sized batteryconstructed using the construction shown in FIG. 8A, has a collectorassembly volume that is 2 percent of the total volume when the can wallsare 10 mils thick and 8 mils thick. The C, AA, and AAA sized batterieshaving similar construction also exhibited significant improvements ininternal volume efficiency, as is apparent from the table in FIGS. 14A.

Beverage Can-Type Construction

The use of the pressure relief mechanism illustrated in FIGS. 8A-10,further allows the use of the beverage can-type construction shown inFIG. 11. The beverage can-type construction shown differs from otherforms of battery seal constructions in that it does not require any formof nylon seal to be inserted into the open end of can 412. Instead,negative outer cover 445 is secured to the open end of can 412 using asealing technique commonly used to seal the top of a food or beveragecan to the cylindrical portion of the can. Such sealing constructionshad not previously been considered for use in sealing batteries becausethey would not readily allow for the negative outer cover to beelectrically insulated from the can.

The method of making a battery having the construction shown in FIG. 11is described below with reference to FIGS. 12A-12D. Prior to attachingnegative outer cover 445 to the open end of can 412, a collector nail440 is welded to the inner surface of cover 445. Next, as shown in FIG.12A, the inner surface of cover 445, as well as the peripheral portionof the upper surface of cover 445, is coated with a layer 475 ofelectrical insulation material, such as an epoxy, nylon, Teflon®, orvinyl. The portion of collector nail 440 that extends within the voidarea between the bottom of cover 445 and the top surface of the negativeelectrode/electrolyte mixture 120, is also coated with the electricalinsulation. Additionally, the inner and outer surfaces of can 412 arealso coated in the region of the open end of can 412. Such coatings 475may be applied directly to the can and cover by spraying, dipping, orelectrostatic deposition. By providing such a coating, negative outercover 445 may be electrically insulated from can 412.

By applying the insulation coating to the areas of the can, cover, andcollector nail within the battery that are proximate the void areawithin the battery's internal volume, those areas may be protected fromcorrosion. While a coating consisting of a single layer of the epoxy,nylon, Teflon®, or vinyl materials noted above will function to preventsuch corrosion, it is conceivable that the coating may be applied usinglayers of two different materials or made of single layers of differentmaterials applied to different regions of the components. For example,the peripheral region of the cover may be coated with a single layer ofmaterial that functions both as an electrical insulator and ananti-corrosion layer, while the central portion on the inner surface ofthe cover may be coated with a single layer of a material that functionsas an anti-corrosion layer but does not also function as an electricalinsulator. Such materials may include, for example, asphalt orpolyamide. Alternatively, either one of the can or cover may be coatedwith a material that functions as both an electrical insulator andanti-corrosion layer, while the other of these two components may becoated with a material that functions only as an anti-corrosion layer.In this manner, the electrical insulation would be provided where needed(i.e., between the cover/can interface), while the surfaces partiallydefining the void area in the internal volume of the cell will still beprotected from the corrosive effects of the electrochemical materialswithin the cell. Further, by utilizing different materials, materialsmay be selected that are lower in cost or exhibit optimalcharacteristics for the intended function.

To assist in the sealing of outer cover 445 to can 412, a conventionalsealant 473 may be applied to the bottom surface of peripheral edge 470of cover 445. Once the sealing procedure is complete, sealant 473migrates to the positions shown in FIG. 12D.

Once collector nail 440 has been attached to outer cover 445 and theelectrical insulation coating has been applied, outer cover 445 isplaced over the open end of can 412 as shown in FIG. 12B. Preferably,can 412 has an outward extending flange 450 formed at its open end.Further, outer cover 445 preferably has a slightly curved peripheraledge 470 that conforms to the shape of flange 450. Once outer cover 445has been placed over the open end of can 412, a seaming chuck 500 isplaced on outer cover 445, such that an annular downward extendingportion 502 of seaming chuck 500 is received by an annular recess 472formed in outer cover 445. Next, a first seaming roll 510 is moved in aradial direction toward the peripheral edge 470 of outer cover 445. Asfirst seaming roll 510 is moved toward peripheral edge 470 and flange450, its curved surface causes peripheral edge 470 to be folded aroundflange 450. Also, as first seaming roll 510 moves radially inward,seaming chuck 500, can 412, and outer cover 445 are rotated about acentral axis, such that peripheral edge 470 is folded around flange 450about the entire circumference of can 412. Further, as first seamingroll 510 continues to move radially inward, flange 450 and peripheraledge 470 are folded downward to the position shown in FIG. 12C.

After peripheral edge 470 and flange 450 have been folded into theposition shown in FIG. 12C, first seaming roll 510 is moved away fromcan 412, and a second seaming roll 520 is then moved radially inwardtoward flange 450 and peripheral edge 470. Second seaming roll 520 has adifferent profile than first seaming roll 510. Second seaming roll 520applies sufficient force against flange 450 and peripheral edge 470 topress and flatten the folded flange and peripheral edge against theexterior surface of can 412, which is supported by seaming chuck 500. Asa result of this process, the peripheral edge 470 of can 412 is foldedaround and under flange 450 and is crimped between flange 450 and theexterior surface of the walls of can 412, as shown in FIGS. 11 and 12D.A hermetic seal is thus formed by this process.

To illustrate the hermetic nature of this type of seal, a D sized canconstructed in accordance with this embodiment of the present inventionwas filled with water as was a D sized can constructed with aconventional seal, such as that illustrated in FIG. 1. The two cans weremaintained at 71° C. and weighed over time to determine the amount ofwater lost from the cans. The conventional construction lost 270 mg perweek, and the construction in accordance with the present invention didnot lose any weight over the same time period. These results wereconfirmed using KOH electrolyte, with the conventional constructionlosing 50 mg per week and the inventive construction again not losingany weight.

As will be apparent to those skilled in the art, the beverage can-typeconstruction utilizes minimal space in the battery interior, reduces thenumber of process steps required to manufacture a battery, andsignificantly reduces the cost of materials and the cost of themanufacturing process. Further, the thickness of the can walls may besignificantly reduced to 6 mils or less. As a result, the internalvolume available for containing the electrochemically active materialsmay be increased. For example, for a D sized battery, the percentage ofthe total battery volume that may be used to contain theelectrochemically active materials may be as high as 97 volume percent,while collector assembly volume may be as low as 1.6 volume percent. Thevolumes of batteries of other sizes are included in the table shown inFIGS. 14A and 14B.

By utilizing the inventive sealing constructions, not only can the canwall thickness be decreased, but also the number of possible materialsused to form the can may be increased due to the lessened strengthrequirements that must be exhibited by the can. For example, theinventive constructions noted above may enable aluminum or plastics tobe used for the can rather than the nickel-plated steel currently used.

A variation of the beverage can construction is shown in FIG. 13. In theillustrated embodiment, the battery can is first formed as a tube withtwo open ends. The tube may be extruded, seam welded, soldered,cemented, etc., using conventional techniques. The tube may be formed ofsteel, aluminum, or plastic. As shown in FIG. 13, the tube defines theside walls 614 of can 612. A first open end of the tube is then sealedby securing an inner cover 616 thereto using the beverage can sealingtechnique outlined above, with the exception that no electricalinsulation is required between inner cover 616 and side walls 614. Apositive outer cover 618 may be welded or otherwise secured to the outersurface of inner cover 616. The battery may then be filled and anegative outer cover 645 may be secured to the second open end of can612 in the same manner as described above.

Printed Label on Can

As noted above, the inventive battery constructions may be used incombination with a printed label, rather than the label substratescurrently used. Current label substrates have thicknesses on the orderof 3 mils. Because such label substrates overlap to form a seam runningalong the length of the battery, these conventional labels effectivelyadd about 10 mils to the diameter and 13 mils to the crimp height of thebattery. As a result, the battery can must have a diameter that isselected to accommodate the thickness of the label seam in order to meetthe ANSI size standards. However, by printing a lithographed labeldirectly on the exterior surface of the can in accordance with thepresent invention, the diameter of the can may be correspondinglyincreased approximately 10 mils. Such an increase in the diameter of thecan significantly increases the internal volume of the battery. All ofthe batteries listed in the tables of FIGS. 14A and 14B, with theexception of the beverage can constructions, include substrate labels.The internal volume of the batteries with substrate labels can befurther increased 2 percent (1.02 cc) for a D sized battery, 2.6 percent(0.65 cc) for a C sized battery, 3.9 percent (0.202 cc) for an AA sizedcell, and 5.5 percent (0.195 cc) for an AAA sized battery, if the labelswere printed directly on the exterior of the can. Labels may also beprinted on the can using transfer printing techniques in which the labelimage is first printed on a transfer medium and then transferreddirectly onto the can exterior. Distorted lithography may also be usedwhereby intentionally distorted graphics are printed on flat material soas to account for subsequent stress distortions of the flat material asit is shaped into the tube or cylinder of the cell can.

Prior to printing the lithographed label, the exterior surface of thecan is preferably cleaned. To enhance adherence of the print to the can,a base coat of primer may be applied to the exterior surface of the can.The printed label is then applied directly on top of the base coat onthe can by known lithography printing techniques. A varnish overcoat ispreferably applied over the printed label to cover and protect theprinted label, and also to serve as an electrical insulating layer. Theprinted label may be cured with the use of high temperature heating orultraviolet radiation techniques.

With the use of the printed label, the thickness of a conventional labelsubstrate is significantly reduced to a maximum thickness ofapproximately 0.5 mil. In particular, the base coat layer has athickness in the range of about 0.1 to 0.2 mil, the print layer has athickness of approximately 0.1 mil, and the varnish overcoat layer has athickness in the range of about 0.1 to 0.2 mil. By reducing the labelthickness, the can can be increased in diameter, thereby offering anincrease in available volume for active cell materials while maintaininga predetermined outside diameter of the battery.

Beverage Can With Feed Through Collector

Referring to FIG. 15, an electrochemical cell 700 is shown constructedwith a feed through collector according to a seventh embodiment of thepresent invention. Similar to the electrochemical cell 400 with beveragecan-type construction shown in FIG. 11, electrochemical cell 700includes an electrically conductive can 712 having a closed end 314 andan open end in which a low volume collector assembly 725 and outernegative cover 750 are assembled. Electrochemical cell 700 includes apositive electrode 115 in contact with the interior walls of can 712 andin contact with a separator 117 that lies between a positive electrode115 and a negative electrode 120. The positive electrode 115 is alsoreferred to herein as the cathode, while the negative electrode 120 isalso referred to herein as the anode. It should be appreciated that thetype of materials and their location internal to the electrochemicalcell may vary without departing from the teachings of the presentinvention.

Electrochemical cell 700 also includes a pressure relief mechanism 370formed in the closed end 314 of can 712. This allows for employment ofthe low volume collector assembly 725 which consumes less volume thanconventional collector assemblies, and therefore achieves enhancedinternal cell volume efficiency. The pressure relief mechanism 370 maybe formed as a groove as described herein in connection with FIGS. 8A,8B, 9, and 10. In addition, a positive outer cover 311 is connected tothe closed end of can 712 and overlies the pressure relief mechanism370. The assembly and location of positive outer cover 311 is providedas shown and described herein in connection with FIG. 8A.

Electrochemical cell 700 includes a collector assembly 725 which closesand seals the open end of can 712. Collector assembly 725 includes acollector nail 740 disposed in electrical contact with the negativeelectrode 120. Also included in the collector assembly 725 is a first orinner cover 745 having a central aperture 751 formed therein. Thecollector nail 740 is disposed and extends through the aperture 751 ininner cover 745. A dielectric insulating material 744 is disposedbetween collector nail 740 and first cover 745 to provide dielectricinsulation therebetween. Accordingly, the collector nail 740 iselectrically isolated from inner cover 745. Dielectric insulatingmaterial 744 is an organic macromolecular material, such as an organicpolymer, and may include an epoxy, rubber, nylon, or other dielectricmaterial that is resistant to attack by KOH and is non-corrosive in thepresence of potassium hydroxide in an alkaline cell. The dielectricinsulating material is assembled as explained hereinafter.

Inner cover 745 in turn is connected and sealed to the open top end ofcan 712. Inner cover 745 may be inserted into can 712 and sealed to can712 by forming a double seam closure at the peripheral edges 450 and 470as explained herein in connection with FIGS. 11-13. While a double seamcan-to-cover closure is shown in connection with the seventh embodimentof the present invention, it should be appreciated that othercan-to-cover closures may be employed, without departing from theteachings of the present invention.

The electrochemical cell 700, according to the seventh embodiment allowsfor a direct connection between can 712 and inner cover 745, whichpreferably provides a pressure seal therebetween, but does not requireelectrical isolation between inner cover 745 and the side walls of can712. Instead, the collector nail 740 is dielectically insulated frominner cover 745 such that the negative and positive terminals of theelectrochemical cell are electrically isolated from one another. Whilethere is no requirement of maintaining electrical isolation between thecan 712 and inner cover 745, it is preferred that a sealant be appliedat the closure joining the can to the cover to adequately seal the can.A suitable sealant may be applied as explained in connection with thebattery shown and described herein in connection with FIGS. 11-12D. Itshould be appreciated that the sealed closure along with the insulatingmaterial should be capable of withstanding internal pressure buildupgreater than the venting pressure at which pressure release mechanism370 releases pressure.

To provide an acceptable outer battery terminal in accordance with wellaccepted battery standards, the electrochemical cell 700 furtherincludes an outer cover 750 in electrical contact with collector nail740. Outer cover 750 may be welded by spot weld 742 or otherwiseelectrically connected to collector nail 740. To insure properelectrical insulation between outer cover 750 and inner cover 745, adielectric material such as annular pad 748 is disposed between outernegative cover 750 and inner cover 745. Suitable dielectric materialsmay include nylon, other elastomeric materials, rubber, and epoxyapplied on the top surface of inner cover 745 or on the bottom surfaceof outer cover 750. Accordingly, an acceptable standard battery terminalmay be provided at the negative end of electrochemical cell 700.

The assembly of electrochemical cell 700 according to the seventhembodiment of the present invention is illustrated in the assembly viewof FIG. 16 and is further illustrated in the flow diagram of FIG. 17.The method 770 of assembly of electrochemical cell 700 includesproviding can 712 formed with a closed bottom end and open top end. Step774 includes disposing into can 712 the active electrochemical materialsincluding the negative electrode, the positive electrode, and anelectrolyte, as well as the separator and other cell additives. Once theactive electrochemical cell materials are disposed within can 712, can712 is ready for closure and sealing with the collector assembly 725.Prior to closing the can, the collector assembly is assembled by firstdisposing the collector nail 740 within aperture 751 formed in innercover 745 along with a ring of insulating material according to step776. Collector nail 740 is disposed in the opening 742 of insulatingring 744 which may include a ring or disk of epoxy which providesdielectric insulation and can be heated to reform and settle between theinner cover 745 and collector nail 740. Alternately, other organicmacromolecular dielectric insulation materials may be used in place ofepoxy, such as a rubber grommet, an elastomeric material, or otherdielectric materials that may form adequate insulation between collectornail 740 and inner cover 745. Also shown formed in inner cover 745 is arecess 755 formed in the top surface and centered about aperture 751.

According to the preferred embodiment, ring 744 of insulating materialis disposed in recess 755 on top of inner cover 745 and the top head ofcollector nail 740 is disposed thereabove. In step 778, the insulatingring 744 is assembled to collector nail 740 and cover 745 and theinsulating ring 744 is heated to a temperature sufficiently high enoughto melt ring 744 such that ring 744 reforms and flows into the aperture751 in cover 745 to provide continuous dielectric insulation betweencollector nail 740 and inner cover 745. For a ring 744 made of epoxy, atemperature of 20° C. to 200° C. for a time of a few seconds totwenty-four hours may be adequate to reform and cure the insulatingmaterial. Once dielectric material 744 forms adequate insulation betweencollector nail 740 and inner cover 745, the insulated material ispreferably cooled in step 780. During the heating and cooling steps 778and 780, the collector nail 740 is centered in aperture 751 such thatnail 740 does not contact cover 745. Thereafter, in step 782, anelectrical dielectric insulating pad 748 such as an annular dielectricpad is disposed on top of inner cover 745 and extends radially outwardfrom the perimeter of nail 740. In step 784, disposed on top ofcollector nail 740 and pad 748 is a conductive negative cover 750 whichis welded or otherwise formed in electrical contact with collector nail740. Once the collector assembly is fully assembled, the collectorassembly is then connected to the can to sealingly close the open end asprovided in step 786. Can closure may employ a double seam closure orother suitable can closure technique. In addition, the assembly method770 includes step 788 of connecting a second outer cover to the closedend of the can, preferably overlying the pressure relief mechanism 370.

While the present invention has been described above as having primaryapplicability to alkaline batteries, it will be appreciated by thoseskilled in the art that similar benefits may be obtained be employingthe inventive constructions in batteries utilizing other electrochemicalsystems. For example, the inventive constructions may be employed inprimary systems such as carbon-zinc and lithium based batteries and inrechargeable batteries, such as NiCd, metal hydride, and Li basedbatteries. Further, certain constructions of the present invention maybe used in raw cells (i.e., cells without a label as used in batterypacks or multi-cell batteries). Additionally, although the presentinvention has been described above in connection with cylindricalbatteries, certain constructions of the present invention may beemployed in constructing prismatic cells.

The above description is considered that of the preferred embodimentsonly. Modifications of the invention will occur to those skilled in theart and to those who make or use the invention. Therefore, it isunderstood that the embodiments shown in the drawings and describedabove are merely for illustrative purposes and not intended to limit thescope of the invention, which is defined by the following claims asinterpreted according to the principles of patent law, including theDoctrine of Equivalents.

The invention claimed is:
 1. A battery comprising: a can for containingelectrochemically active materials including positive and negativeelectrodes and an electrolyte, said can having a first end, an opensecond end, side walls extending between said first and second ends, andan end wall extending across said first end; a pressure relief mechanismformed in said end wall of said can for releasing internal pressure fromwithin said can when the internal pressure becomes excessive; a firstouter cover positioned on said end wall of said can to be in electricalcontact therewith and to extend over said pressure relief mechanism; asecond outer cover positioned across the open second end of said can;and an insulator disposed between said can and said second outer coverfor electrically insulating said can from said second outer cover,wherein said first outer cover includes a protrusion extending over andspaced from said pressure relief mechanism, and the protrusion providesan open space over said pressure relief mechanism so that said firstouter cover does not interfere with said pressure relief mechanism. 2.The battery as defined in claim 1, wherein said insulator is a coatingof insulating material deposited on at least one of said can and saidsecond outer cover.
 3. The battery as defined in claim 1, wherein saidend wall is integrally formed with said side walls of said can.
 4. Thebattery as defined in claim 1, wherein said can is formed as a tube withsaid end wall secured across said first end.
 5. The battery as definedin claim 1, wherein said pressure relief mechanism is formed by coininga surface of said end wall of said can.
 6. The battery as defined inclaim 1, wherein said pressure relief mechanism includes an arc-shapedgroove formed in a surface of said end wall of said can.
 7. The batteryas defined in claim 6, wherein said arc-shaped groove is formed as a 300degree partial circle.
 8. The battery as defined in claim 1, whereinsaid first outer cover is electrically coupled to said positiveelectrode to serve as a positive external battery terminal and saidsecond outer cover is electrically coupled to said negative electrode toserve as a negative external battery terminal.
 9. The battery as definedin claim 8 wherein said first outer cover includes a centrally disposedcontact terminal protrusion, and wherein said pressure relief mechanismis formed in said end wall of said can in a region underlying saidprotrusion.
 10. The battery as defined in claim 1, wherein said pressurerelief mechanism includes a hinged portion that pivots out from said endwall of said can upon rupture.
 11. A battery comprising: a containercontaining electrochemically active materials including positive andnegative electrodes and an electrolyte, said container having an openend, a closed end, and side walls extending between the open and closedends; a pressure relief mechanism formed in the closed end of saidcontainer for releasing internal pressure from within said containerwhen the internal pressure becomes excessive; a first outer coverpositioned on said closed bottom end of said container and extendingover said pressure relief mechanism; and a second outer cover positionedacross said open end of said container, wherein said first outer coverincludes a centrally disposed contact terminal protrusion, said pressurerelief mechanism is formed in said closed end of said container in aregion underlying said protrusion, said centrally disposed contactterminal is spaced from said pressure relief mechanism, and saidprotrusion provides an open space over said pressure relief mechanism sothat said first outer cover does not interfere with said pressure reliefmechanism.
 12. The battery as defined in claim 11, wherein saidcontainer comprises a conductive can, said first and second outer coverscomprise conductive material, and an insulator is disposed between saidcan and said second outer cover for electrically insulating said canfrom said second outer cover.
 13. The battery as defined in claim 11,wherein said pressure relief mechanism includes an arc-shaped grooveformed in said bottom end of said container.
 14. A method of assemblinga battery comprising the steps of: forming a can having an open end anda closed end; forming a pressure relief mechanism by forming a groove ina surface of the closed end of the can; forming a first outer cover anda second outer cover; dispensing electrochemically active materials inthe can; sealing the first outer cover across the open end of the can;and attaching the second outer cover to the closed end of the can suchthat the second outer cover extends over the pressure relief mechanism.15. The method of claim 14, wherein said step of sealing includingproviding a layer of electrical insulation provided between.